1. Field of the Invention
The invention relates to hydrophilic synthetic resins, esterified for stability to hydrolysis, for use in aqueous systems; to a process for their preparation; and to their use.
The hydrolytically-stable hydrophilic synthetic resins of the present invention or an aqueous system produced from the synthetic resin of the present invention, are useful as an additive for aqueous coating systems, inks, including printing inks, and/or color pastes, as thickeners, as dispersing auxiliaries for inorganic and organic pigments, for increasing the solids content of coating systems, for improving the gloss and fullness, for increasing the hardness of the coating, for improving the flow and the adhesion of coatings to metallic substrates, and as agents for the more rapid drying of coating systems for a more rapid decrease in surface tack.
2. Discussion of the Background
Novel synthetic resins are obtained by reacting a hydroxyl-containing ketone, ketone/aldehyde or urea/aldehyde synthetic resins or hydrogenated products of the synthetic resins thereof, such as described in Ullmann's Encyclopedia of Industrial Chemistry, VCH Verlagsgesellschaft mbH, Weinheim 1993, Vol. 23, pp. 99-105 with a polycarboxylic acid and/or a polycarboxylic anhydride; the reaction of the above synthetic resin with a carboxylic acid or anhydride is controlled to such an extent only, so that chemical attachment takes place only via a limited fraction of the existing or potential acid functions, leaving other carboxyl functions unreacted as hydrophilic groups and thus providing for the solubility in water, dilutability in water or dispersibility in water of the synthetic resin hydrophilically modified in this way.
The prior art discloses, in general terms, the hydrolytically-stable addition of hydrophilic carboxyl groups, with the aid of, for example, maleic anhydride, onto resins containing appropriate conjugated or isolated double bonds by a quite different reaction route, by way of a Diels-Alder reaction (DE 24 41 935) and not by esterification. Consequently, the technique of DE 24 41 935 is restricted to synthetic resins which are able to undergo a Diels-Alder reaction.
DE 25 42 090 describes water-soluble compounds which carry sulfonic acid groups and which, in deviation from the novel process, are obtainable in a conjoint condensation reaction from cycloalkanone, formaldehyde and alkali metal bisulfite.
DE 31 44 673 indicates water-soluble condensation products which are likewise obtained by conjoint reaction of ketones, aldehydes and compounds which introduce acid groups. Examples of the latter are sulfites and salts of amidosulfonic acid, aminoacetic acid or phosphorous acid. Both processes, of DE 25 42 090 and DE 31 44 673, give products with a disadvantageous high electrolyte content (e.g. Na+) which can therefore not be employed in coating systems, because the high electrolyte content reduces the important corrosion protection afforded by coatings.
DE 34 06 473 and DE 34 06 474, or EP 0 154 835, describe a process for preparing stable aqueous dispersions of urea/aldehyde resins, or, respectively, ketone/(aldehyde) resins, according to which the resin melt or a highly concentrated solution thereof, is dispersed in water in the presence of organic protective colloids and with or without the addition of an emulsifier.
A disadvantage of these processes according to DE 34 06 473 and DE 34 06 474 is that the organic protective colloids and, if used, emulsifiers interfere with the use of the aqueous ketone/(aldehyde) and urea/aldehyde synthetic resins in the coatings sector: the hydrophilic protective colloids and, if used, emulsifiers remain in the coating and thus render the coating sensitive to moisture; as a result, the coating swells under the effect of moisture, loses hardness and suffers a loss of some of its corrosion protection effect.
Whereas water-insoluble ketone, ketone/aldehyde and urea/aldehyde synthetic resins and the hydrogenated products thereof have been known for a long time (cf. Ullmann's Encyclopedia of Industrial Chemistry, VCH Verlagsgesellschaft mbH, Weinheim 1993, Vol. 23, pp. 99-105), no disclosures have been made of hydrolytically-stable ketone, ketone/aldehyde and urea/aldehyde synthetic resins, esterified with polycarboxylic acids and/or polycarboxylic anhydrides, or the hydrogenated products of such synthetic resins, for use in aqueous systems.